Wireless Sensor Interface with Mobile Terminal Satellite Modem and Global Location System

ABSTRACT

A system and method for implementing a low-power local-area wireless network for use with a mobile terminal satellite modem. This low-power local-area wireless network enables sensors on an asset to wirelessly transmit sensor data to a mobile terminal affixed on the asset. The mobile terminal reports the sensor data along with asset position information to a centralized facility via a communications satellite.

This application is a continuation of non-provisional patent applicationNo. 13/037,449, filed Mar. 1, 2011, which is a continuation ofnon-provisional patent application No. 12/333,048, filed Dec. 11, 2008,which is a continuation of U.S. Pat. No. 7,468,927, issued Dec. 23,2008, which claims priority to provisional application No. 60/715,596,filed Sep. 12, 2005, and provisional application No. 60/721,540, filedSep. 29, 2005. The above-identified applications and patents are eachincorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates generally to asset tracking and monitoringand, more particularly, to a wireless sensor interface with mobileterminal satellite modem and global location system.

2. Introduction

Tracking mobile assets represents a growing enterprise as companies seekincreased visibility into the status of a service fleet (e.g., long-hauldelivery fleet). Visibility into the status of a service fleet can begained through mobile terminals that are affixed to service vehicles.These mobile terminals can be designed to generate position informationthat can be used to update status reports that are provided to customerrepresentatives.

In providing status reports to a centralized facility, the mobileterminal can generate position information through the reception ofsatellite position signals such as that generated by the GPS satellitenetwork. Generated status reports are transmitted to the centralizedfacility using a return link via a communications satellite.

In various embodiments, the status reports can also include sensor datathat is generated by sensors affixed to the service vehicle (e.g.,inside a trailer). This sensor data would enable the company to discernthe condition of cargo being transported, the condition of the servicevehicle, the occurrence of any events at the service vehicle, etc.

Sensor data can be obtained using sensors that are positioned at variouspoints on a service vehicle. Connection of this collection of sensors tothe mobile terminal can represent a substantial expense. Accordingly,what is needed is a mechanism that reduces the costs of obtaining suchsensor data, while also minimizing the overall power required by themonitoring system.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

FIG. 1 illustrates an embodiment of a satellite communications networkthat enables the monitoring of remote assets using a collection ofsensors.

FIG. 2 illustrates an embodiment of a wireless local area network.

FIG. 3 illustrates a flowchart of a process of reporting sensor data toa centralized facility.

FIG. 4 illustrates an embodiment of a wireless device that is coupled toa sensor.

FIG. 5 illustrates a flowchart of a process of communication method thatconserves power.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

Conventional asset tracking systems have been used to track thepositions of assets. This position information can be relayed viasatellite to a centralized facility that is responsible for reportingthe current and historical positions of those assets. In meeting thedemand by customers for greater visibility into the status of theassets, the asset-tracking system can also include one or more sensorsthat are affixed to those assets. Various sensor types can be used. Forexample, volume sensors, temperature sensors, chemical sensors,radiation sensors, weight sensors, light sensors, water sensors, etc.can be used to report the condition of cargo being transported. Inanother example, truck cab ID indicators, odometer sensors, wheelsensors, vibration sensors, etc. can be used to report the condition ofthe service vehicle. In general, these various sensors can be used toreport status information or the occurrence of any events at the servicevehicle.

Mounting one or more sensors within a trailer is especially valuablewhen considering the cargo that is being transported. These sensors canprovide valuable information relating to the existence, condition of,and access to such cargo. For this reason, significant efforts have beenmade to capture and report sensor data to a centralized facility.

To enable the reporting of sensor data along with position information,sensors need an interface to a mobile terminal that reports the positionand sensor information via wireless communication (e.g., satellitecommunication) to a centralized facility. The interface between thesensors and the mobile terminal represents a significant technical andeconomic challenge.

Consider, for example, an implementation where the mobile terminal ismounted on the roof of a trailer. In this implementation, the mobileterminal could require extensive connections to sensors that can bepositioned at various points on the cab/trailer (e.g., on the trailerdoor, inside the trailer, on the wheels, in the cab, etc.). As would beappreciated, cable connections between this mobile terminal and thevarious sensors can add a substantial expense (e.g., hundreds ofdollars) to the overall cost of deployment.

The cable connections can also represent technical challenges. Forexample, cable connections between a roof-mounted mobile terminal and asensor located inside the trailer would require that one or more holesbe cut into the trailer compartment. While these holes would facilitatethe passage of sensor cabling into the trailer compartment, the holeswould also raise significant weatherproofing issues. Moreover, the holescould also raise insulation issues when considering refrigerated trailercompartments. In another example, cable connections between aroof-mounted mobile terminal and a sensor located in the cab wouldrequire additional cabling or integration within existing cabling suchas the cab-trailer electrical interface.

As these examples illustrate, implementing connections between a mobileterminal and one or more sensors affixed to the tracked asset can resultin significant cost and/or development issues. The principles of thepresent invention are designed to meet these needs by not onlyimplementing a wireless connection between a mobile terminal and one ormore sensors that facilitates two-way communication, but also operatingsuch a wireless network in manner that minimizes the power required themobile terminal and sensor devices.

Prior to describing the details of the principles of the presentinvention, a description of an embodiment of an operational context isfirst provided. FIG. 1 illustrates an embodiment of a satellite network100 that includes operations gateway 102, communicating with mobileterminal 120 on an asset. Communication between operations gateway 102and mobile terminal 120 is facilitated by satellite gateway 104 at theground station and satellite modem 122 in mobile terminal 120. Bothsatellite gateway 104 and satellite modem 122 facilitate communicationusing one forward and one return link (frequency) over communicationssatellite 106.

In one embodiment, the satellite communication is implemented in a timedivision multiple access (TDMA) structure, which consists of 57600 timeslots each day, per frequency or link, where each slot is 1.5 secondslong. On the forward link, operations gateway 102 sends a message orpacket to mobile terminal 120 on one of the 1.5 second slots. Uponreceipt of this message or packet, mobile terminal 120 would thenperform a GPS collection (e.g., code phase measurements) using GlobalLocating System (GLS) module 124 or to perform sensor measurements andtransmit the data back to operations gateway 102 on the return link, onthe same slot, delayed by a fixed time defined by the network. In oneembodiment, the fixed delay defines a length of time that enables mobileterminal 120 to decode the forward packet, perform the data collectionand processing, and build and transmit the return packet.

In one embodiment, mobile terminal 120 can be configured to produceperiodic status reports. In this configuration, mobile terminal 120would wake up periodically, search for its assigned forward slot,perform data collection and processing, and transmit the status reporton the assigned return slot. In another embodiment, mobile terminal 120can be configured to produce a status report upon an occurrence of anevent (e.g., door opening, motion detected, sensor reading, etc.). Inthis configuration, mobile terminal 120 would wake up upon occurrence ofan event, search for an available forward slot, perform data collectionand processing, and transmit the status report on the return slotcorresponding to the identified available forward slot.

Upon receipt of a status report from mobile terminal 120, operationsgateway 102 passes the information to operations center 112, where theinformation is processed and passed to a customer via the Internet. Adetailed description of this communications process is provided in U.S.Pat. No. 6,725,158, entitled “System and Method for Fast AcquisitionPosition Reporting Using Communication Satellite Range Measurement,”which is incorporated herein by reference in its entirety. As would beappreciated, the principles of the present invention can also be appliedto other satellite communications systems as well as to terrestrialcommunications systems.

As FIG. 1 further illustrates, mobile terminal 120 can also collectsensor measurements from sensors 130 that are positioned at variouspoints on the asset being tracked. Transmission of sensor informationfrom sensors 130 to mobile terminal 120 is facilitated by a low-power,low-cost wireless interface. As illustrated the wireless interface useswireless device WD(1) that is coupled to satellite modem 122, andwireless devices WD(2)-WD(n) that are coupled to respective sensors 130.The wireless network formed by wireless devices WD(1)-WD(n) enablesmobile terminal 120 to interface to the plurality of wireless sensors130. It should be noted that this wireless network can operateindependently from the standard functions of mobile terminal 120.

In one embodiment, wireless device WD(1) is integrated on the samehardware as satellite modem 122. In an alternative embodiment, wirelessdevice WD(1) is on separate hardware from satellite modem 122 and uses ahardwired interface such as a serial communications interface.

In one embodiment, the wireless interface uses wireless devices that canbe configured as master or slave devices. FIG. 2 illustrates anembodiment of a master-slave configuration for the wireless devices. Asillustrated, wireless device WD(1) in mobile terminal 120 is configuredas a master device, while wireless devices WD(2)-WD(n) that are coupledto individual sensors are configured as slave devices. This master-slaveconfiguration enables independent communication between the wirelessdevices.

Each wireless device can be an independently addressable unit having itsown processor, power management, sleep timers and other apparatus thatallows it to perform low data rate communications, conserve power andreduce cost. It is a feature of the present invention that this wirelessinterface has the capability to transfer binary data in both directionsto and from a sensor device. In one embodiment, slave devices onlytransmit in acknowledgment from a request from a master device. Thistype of half-duplex communication exhibits good performance in low datarate systems and for avoiding collisions.

FIG. 3 illustrates a flowchart of communication between a sensor and thecustomer interface. As illustrated, the process begins at step 302,where a wireless device (e.g., slave wireless device WD(2)) collectsdata from an attached sensor 130. In one embodiment, this datacollection is facilitated by a hardwired interface, such as a serialinterface. In an alternative embodiment, the sensor is integrated withthe wireless device.

After the sensor data is collected by the wireless device, at step 304,the wireless device then transmits the sensor data to the mobileterminal wireless device (e.g., master wireless device WD(1)). At step306, the mobile terminal wireless device then forwards the informationto satellite modem 122. At step 308, satellite modem 122 transmits theinformation to satellite gateway 104 via satellite 106. From here, atstep 310, the sensor data can then be made available to the customerover a customer interface via the Internet.

As noted, it is a feature of the present invention that data can also besent to the sensor device. For example, a customer can send data to asensor device from the web interface in the opposite direction of thatdescribed in the process of FIG. 3. This direction of communication tothe sensor device enables the customer or system operator to configurethe sensor device through a wireless interface. In this context, deviceconfiguration can include, but is not limited to, its operating mode(such as master or slave device), baud rate, power level, channelselection, wake up interval, status requests, etc. In general, all ofthe wireless interface network's configurable parameters can be set orchanged either over-the-air from the gateway, or through some otherinterface, such as a wired interface using a configuration terminal.

In addition to enabling bi-directional communications to and from asensor device, it is a feature of the present invention that the localarea wireless interface can enable system devices to be in a low powersleep mode most of the time, and only transmit for a short duration oftime on a specified frequency or channel to conserve power. In oneembodiment, the local area wireless interface uses a TDMA typecommunication protocol.

FIG. 4 illustrates an embodiment of a wireless device that has theability to enter a low power state, and wake at a programmed time. Asillustrated, wireless device 400 includes microprocessor 402, which isused to control the various functions, power management 404, which isused to power down and enter a low power state, real time clock 406,which wakes or powers-up the unit at a pre-determined time, input/output408, which allows an interface to other devices, sensors, transducers,including the mobile terminal, and RF module 410, which performs theactual wireless communications. RF module 410 can be simple or complex.In one embodiment, RF module 410 would include a computer, a low-layerwaveform and modulation technique, and its own protocol that coulddetect and correct errors and perform retries in order to reliablytransmit and receive data.

Having described an embodiment of a wireless device, an example of adata transfer over the low-power local-area wireless network is nowprovided with reference to the flowchart of FIG. 5. As illustrated, theprocess begins at step 502 where master device (e.g., WD(1)) is awakenedand receives data from its I/O port for a particular slave device (e.g.,WD(2)) and a sensor 130 that is attached to that slave device. Themaster device prepares this information for delivery and stores it. Atstep 504, the master device then programs a sleep timer to wake at thecorrect time then powers down. This wake time is the time the masterdevice and the network protocol expects the receiving slave device towake, assuming it is synchronized to the network. The master device canalso compensate for time drifts and other physical layer issues.

At step 506, the master unit awakens at the scheduled time and transmitsthe information to the slave device. At step 508, the master device thendetermines whether an acknowledgment is received. In one embodiment, theslave device responds immediately. In another embodiment, both themaster and slave device go back into a sleep mode and wake shortlythereafter for the slave device to send the acknowledgement.

If it is determined, at step 508, that the acknowledgment is notreceived, then the protocol would instruct both master and slave devicesto try again at a later prescribed time, or wait for the next scheduledwakeup interval, depending on it configuration. If it is determined, atstep 508, that the acknowledgment is received, then the data transferprocess ends and the slave device would deliver the data to its attachedsensor through its I/O port.

In one example, this process can be used to transmit configurationinformation to a sensor device. In another example, this process can beused to transmit a status request to a sensor device, wherein the sensordevice's response would include measurement data taken by the sensor.This example illustrates an example of scheduled reporting throughpolling of the sensor device.

Event reporting can also be supported by the network protocol. Here, asensor event can represent a detected change in monitored status (e.g.,door opening, emptying of cargo, change in temperature, etc.), adetected change in operating state, or any other change detectable by asensor. Information reflective of this detected event can then beprepared for transmission to the master device by the slave device,wherein the slave device sleeps until a scheduled time for transmissionto the master device.

As described, the network protocol would enable the master and slavedevices to sleep until a scheduled time when communication between thepair of devices on a known channel or frequency is expected to occur.This scheduled time would support a short communication between the twodevices, which would ensure that the devices are only awakened for aminimal amount of time. The remaining time, which represents the vastmajority of time, would be spent in a low power sleep mode.

In the description above, it is assumed that the network is synchronizedsuch that the wake-up times are known by the individual devices. If thenetwork is not synchronized, or the wake-up times are different, and/orchannels or frequencies are different, the network protocol would entera synchronization mode. In one embodiment, the synchronization processhas all devices wake at some pseudo-random interval and channel untilthey find each other. The data transmitted would be small in order tominimize time and power consumption, while maximizing the probability ofa hit or detection. Also, devices can be designed to slow themselvesdown or backoff after a period of time when it determines it is past thetime where it normally synchronizes. This conserves power especially ifthe device has failed.

The synchronization process can also be expedited given some knowninformation about the other devices that can or should be on the networksuch as their ID or group number. This information can be used in thenetwork protocol, and in the synchronization process, particularly inthe pseudo-random wake-up portion to increase the likelihood of a hit onboth time and frequency. For example, this information can be used toforce all devices onto the same channel or frequency, which eliminatesthe need to search the other frequencies, and reduces thesynchronization time. This information can also be pre-programmed intoeach device during installation. Also, other information can be added atthe factory, such as initializing the real time clocks such that thealgorithm can pick times and frequencies based on the day to increasethe probability of a hit, and reduce synchronization time.Synchronization can be further expedited by extraneous events such asmanually pushing a button at approximately the same time on all deviceson the network to initiate a momentary high rate of retries on thenetwork. This type of event can cause all devices to use onepre-determined frequency and have each device remain poweredcontinuously for a short duration, enough to allow all devices to enterthis state and synchronize. While this mode consumes more power, it onlyneeds to be in this mode for a short time since all the devices knowthat the others are also in this mode and awake.

Once a network is synchronized, the master and the network protocol canassign each device to a particular channel or frequency and wakeup timeor slot. It can also broadcast additional information after the initialsynchronization which will help each device more quickly synchronize inthe future if it loses it's synchronization. The process that maintainssynchronization can also use dithering to vary the wakeup times andfrequencies on each wakeup in order to avoid collisions with othernetworks that may be within the same RF range.

Each individual network can also be designed to communicate to a globalmaster device to send and receive broadcast information. An example of aglobal master device could be a hand-held diagnostic tool that acts as amaster device except that it doesn't sleep and can continuouslybroadcast out to all devices since it has no power constraints. Bycontinuously broadcasting, such a device can quickly reach all thedevices in any network within RF range by waiting until their next wakeup, where they can receive the broadcast information. When a devicewakes on its scheduled time, which is completely different and randomfrom devices on other networks, it can receive the broadcastinformation. This information would instruct the devices on what to do.One example is to command all devices to report their presence andstatus. The protocol can support this type of broadcast by allowingacknowledgements and retries. This way a hand held device can be used,for example, in a trucking yard to detect all networks within the yardto do an inventory. It can also be used to reprogram or reconfigurenetworks. This function of the network protocol allows devices tooperate in different modes in order to perform maintenance, diagnostics,and operations.

As would be appreciated, various network protocols can be designed tooperate the low-power local-area wireless network of the presentinvention. While the network protocol details can vary depending on theimplementation, the network protocol is designed to satisfy a variety offunctions other than the basic communication between master and slavedevices. Some of the functions supported can include transferring datato and from a specific device, communicating scheduled and event data,auto detection of devices, configuring and reading status of devices,allowing diagnostic tools to use the network for configuration andre-programming, error handling, retrying failed communications,detecting collisions or interference from other low-power local-areawireless network, re-synchronizing timing of the devices, andautomatically changing channels or frequencies.

These and other aspects of the present invention will become apparent tothose skilled in the art by a review of the preceding detaileddescription. Although a number of salient features of the presentinvention have been described above, the invention is capable of otherembodiments and of being practiced and carried out in various ways thatwould be apparent to one of ordinary skill in the art after reading thedisclosed invention, therefore the above description should not beconsidered to be exclusive of these other embodiments. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting.

What is claimed is:
 1. A wireless sensor monitoring system at an assetlocation, comprising: a first wireless device that interfaces with awireless modem at said asset location for delivery of sensor data to aremote location; and a second wireless device that is configured toawaken from a low power state to receive a status request from saidfirst wireless device, said second wireless device responding to saidstatus request with measurement data generated by a sensor device thatis associated with said second wireless device.
 2. The system of claim1, wherein said wireless modem is a satellite modem.
 3. The system ofclaim 1, wherein said first wireless device is configured as a masterdevice and said second wireless device is configured as a slave device.4. The system of claim 3, wherein said slave device only transmits inacknowledgment of a request from said master device.
 5. The system ofclaim 3, wherein said first wireless device assigns a communicationchannel and wakeup time to said slave device after said slave devicecompletes a synchronization process.
 6. The system of claim 1, whereinsaid first wireless device wirelessly transmits configurationinformation to said second wireless device.
 7. The system of claim 6,wherein said configuration information originates at a remote locationand is received by said first wireless device via said wireless modem.8. The system of claim 6, wherein said configuration informationincludes an operating mode of said sensor device.
 9. The system of claim6, wherein said configuration information includes a baud rate of saidsensor device.
 10. The system of claim 6, wherein said configurationinformation includes a power level of said sensor device.
 11. The systemof claim 6, wherein said configuration information includes a wake upinterval of said sensor device.
 12. The system of claim 1, wherein saidsecond wireless device is integrated with said sensor device.
 13. Thesystem of claim 1, wherein said second wireless device is coupled tosaid sensor device via a serial interface.
 14. A wireless sensormonitoring system at an asset location, comprising: a locating devicethat is coupled to a wireless modem, said locating device generatinginformation that is used to identify a location of an asset; and a firstwireless device at said asset location for delivery of sensor data to aremote location via said wireless modem, said first wireless devicebeing configured to communicate wirelessly with a second wireless devicethat is configured to awaken from a low power state to receive a statusrequest from said first wireless device, said first wireless devicereceiving, in response to said status request, measurement datagenerated by a sensor device that is associated with said secondwireless device.
 15. The system of claim 14, wherein said locatingdevice receives global positioning system satellite signals.
 16. Thesystem of claim 15, wherein said locating device generates locationinformation that is used, at a location remote from said asset location,to calculate a location of the asset.
 17. The system of claim 14,wherein said first wireless device is integrated in hardware with saidwireless modem.
 18. The system of claim 14, wherein said first wirelessdevice is on separate hardware from said wireless modem, andcommunicates with said satellite modem using a hardwired interface. 19.The system of claim 14, wherein said wireless modem is a satellitemodem.
 20. The system of claim 14, wherein said first wireless deviceassigns a communication channel and wakeup time to said second wirelessdevice after said second wireless device completes a synchronizationprocess.